It seems you are trying with a invalid property name. Instead of Ratings_VotingExperience
use Ratings_x005f_VotingExperience
.
list.RootFolder.Properties["Ratings_x005f_VotingExperience"] = "Likes";
So question is: Where did I get that? In the following end-point:
/_api/Web/GetFolderByServerRelativeUrl('/Lists/{ListName}')/Properties
I have sent a GET request to the above URL
and it returned me something like Ratings_x005f_VotingExperience
.
Update
It's true above thing does not work! So I had a little R&D and made it working. Basically we need to add two site columns in list to make Rating thing working. I got the idea from Rating Settings itself.

Site columns are:
LikesCount
which GUID ID
is 6e4d832b-f610-41a8-b3e0-239608efda41
LikedBy
which GUID ID
is 2cdcd5eb-846d-4f4d-9aaf-73e8e73c7312
PS: These Guids are fixed
So I added these columns using below code and enabled Rating Settings
using(ClientContext clientContext = new ClientContext(targetSite)) {
clientContext.Credentials = onlineCredentials;
Web web = clientContext.Web;
List list = web.Lists.GetByTitle("List Name");
clientContext.Load(list);
clientContext.ExecuteQuery();
var likeCount = web.AvailableFields.GetById(new Guid("6e4d832b-f610-41a8-b3e0-239608efda41"));
var likedBy = web.AvailableFields.GetById(new Guid("2cdcd5eb-846d-4f4d-9aaf-73e8e73c7312"));
clientContext.Load(likeCount, p => p.SchemaXmlWithResourceTokens, p => p.Id, p => p.InternalName, p => p.StaticName);
clientContext.Load(likedBy, p => p.SchemaXmlWithResourceTokens, p => p.Id, p => p.InternalName, p => p.StaticName);
clientContext.ExecuteQuery();
list.Fields.AddFieldAsXml(likeCount.SchemaXmlWithResourceTokens, true, AddFieldOptions.AddFieldInternalNameHint | AddFieldOptions.AddToAllContentTypes);
list.Fields.AddFieldAsXml(likedBy.SchemaXmlWithResourceTokens, false, AddFieldOptions.AddFieldInternalNameHint | AddFieldOptions.AddToAllContentTypes);
list.Update();
clientContext.ExecuteQuery();
}
Above code will enable like/unlike. For other things, we have enable those also. Find here
private readonly Guid RatingsFieldGuid_AverageRating = new Guid("5a14d1ab-1513-48c7-97b3-657a5ba6c742");
private readonly Guid RatingsFieldGuid_RatingCount = new Guid("b1996002-9167-45e5-a4df-b2c41c6723c7");
private readonly Guid RatingsFieldGuid_RatedBy = new Guid("4D64B067-08C3-43DC-A87B-8B8E01673313");
private readonly Guid RatingsFieldGuid_Ratings = new Guid("434F51FB-FFD2-4A0E-A03B-CA3131AC67BA");